Are you trying to give a user the ability to execute DDL in that user's schema? Or to execute DDL in some other user's schema?

DK2010 showed you how to give a user permission to execute DDL in their own schema. Looking at your question, however, my guess is that you are asking about how to give a user privileges to execute DDL in some other schema. You can't grant DDL privileges on individual objects or individual schemas. In theory, you could grant the user appropriate ANY privileges (i.e. CREATE ANY TABLE) but that would give the user the ability to do DDL in any schema in the database. Those are extremely powerful privileges that should only be granted to DBAs.

If you are trying to give a user the ability to execute DDL against a single different schema, can you explain the business problem that you are trying to solve? There are probably other ways of solving whatever business problem you have.